In the field of medicine particulate carriers have been used to deliver medicines to the body and to serve as artificial oxygen carriers (AOC) in artificial blood products. Artificial blood is a product made to act as a substitute for red blood cells which transport oxygen and carbon dioxide throughout the body. However, the function of real blood is complicated, and the development of artificial blood has generally focused on meeting only a specific function, gas exchange—oxygen and carbon dioxide.
In contrast whole blood serves many different functions that has been difficult to duplicate by an AOC. Artificial blood mixable with autologous blood can support patients during surgery and support transfusion services in emerging countries with limited healthcare, blood donations and storage facilities, or high risk of exposure to disease since screening procedures are too expensive. A blood substitute, which is not dependent upon cross matching and blood-typing would mean no delay in blood availability, and could mean the difference between life and death of patients.
Blood donations are in short supply. Another motivation for developing improved AOC is that despite significant advances in donated blood screening there are still concerns over the limited shelf life which is 42 days at 2°-6° C.
Despite significant advances in donated blood screening and storage, concerns about the supply, cost and safety of donated stored blood remain. When testing blood for dangerous pathogens therein there is currently no practical way to test for emerging diseases such as Cruetzfeld-Jacob disease, smallpox and SARS. According to a 2000 NIH study, 10-15 million units of blood are annually transfused throughout the globe without testing for HIV and other diseases. This is particularly true for areas with high HIV-infected population such as South Africa where the percentage of people infected with HIV can be as high as 40 percent. A recent report (Koch C G, Li L, Sessler D I et al., Duration of Red-Cell Storage and Complications after Cardiac Surgery, New Eng. J. of Med. 2008; 358:1229-1239) details ill effects associated with using stored blood for open heart surgery and highlights the urgency to find artificial oxygen carriers (AOC) functioning as artificial blood as an alternative to the donated blood supply.
Chemically and biologically inert, emulsified, sterilized PFCs are stable in storage at low temperatures 2-5° C. for over a year. Further, PFCs are relatively inexpensive to produce and can be made devoid of any biological materials eliminating the possibility of spreading an infectious disease via a blood transfusion. Because they are not soluble in water they must be combined with emulsifiers able to suspend tiny droplets of PFC in the blood. In vivo the perfluorocarbon is ultimately expelled via the lungs after digestion of the emulsifier by the macrophage/monocyte system. In addition, PFCs are biologically inert materials that can dissolve about fifty times more oxygen than blood plasma but less oxygen than red blood cells. For instance, a mixture consisting of 70% blood and 30% perfluorocarbon by volume can provide the needed 5 ml of oxygen per 100 ml of blood if the partial pressure of oxygen in the lungs can be increased to 120 mm Hg by having the patient breath air with an oxygen partial pressure of approximately 180 mm Hg.
In contrast to the above described promising features for PFC based AOCs, use of such PFC-based AOCs has resulted in flu-like symptoms, a need for higher than normal oxygen pressure, problems such as emulsifier toxicity, formation of oxygen free radicals, long term retention of the AOCs in the tissue, damage to lung tissues, a decrease in platelet count, and problems related to loss of nitrous oxide (NO) from circulation in the blood. The loss of NO is also a problem with hemoglobin based AOCs. In addition, recent phase III trials for Oxygent (Alliance Pharmaceutical Corporation, San Diego, Calif.) which uses a stable perfluorooctyl bromide/perfluorodecyl bromide egg yolk phospholipid emulsion and has 4-5 times greater oxygen carrying capacity than Fluosol-DA-20 (Green Cross, Japan) have shown an increased incidence of stroke in treated patients compared to controls, and so trials of Oxygent have been halted.
PFCs dissolve more oxygen than water, but still less than normal blood. To supply the needed amount of oxygen in circulation, patients may require supplemental oxygen. Highly hydrophobic PFC requires emulsifiers to stabilize the droplet in blood. These emulsifiers interact with proteins and emulsifiers found in blood leading to instability. As a result, large quantities of PFC in circulation cannot be tolerated. Small amounts of PFC escape from the blood into the lungs where it is vaporized and breathed out. Large amounts of PFC and emulsifier can have a negative effect on lung function.
Crosslinked, polymerized or encapsulated hemoglobin based AOC are late-corners compared with PFC based AOCs described in previous paragraphs, and are attracting increasing attention because their oxygen delivery characteristics are similar to that of the red blood cells (hereinafter referred to as RBC). Some hemoglobin based AOCs are Hemolink, Hemosol, Optso and Hemospan, Polyheme (Northfield, USA), and Hemopure (Biopure Corp, USA). Some of these are at an advanced stage of development and have passed Phase III trials in Africa and Europe. However, there is a potential to transmit diseases from the animals from which the Hb was obtained and purified, and high production costs have slowed advances. Whether or not other side effects such as iron overload from localized enzymatic digestion in liver will emerge with these Hb based AOCs is still unknown.
Polymeric hemoglobins (pHb) bind O2 and CO2, with a binding mechanism much like that of red blood cells (RBC), but even a small quantity of unpolymerized Hb left in the circulation can become very toxic. As an AOC, a large amount of pHb needs to be injected into a person. Premature breakdown can increase the risk of toxicity, and such a large amount can overtax the body's natural removal processes. Polymerized Hb remains costly. Animal sources of Hb run the risk of transferring, among other things prion-based diseases. Recombinant Hb is a promising approach. It requires high quality separation and purification procedures, that add to the cost.
While both pHb and PFCs based AOC products deliver oxygen in significant quantities to cells and tissue, their side effects, such as nitric oxide related vasoconstriction, stroke, cardiac arrest, flu-like symptoms and long term chemical toxicity, have forced the termination of all the clinical trials in the U.S. An all-out effort to reduce the toxicity of relatively large quantity of AOC injected into a body by metabolic decompositions has failed.
The list of desirable features for safe artificial blood products is long and includes: adequate oxygen uptake in the lungs and delivery to the tissues, corresponding release of oxygen and removal of carbon dioxide from the tissues; wide applicability (i.e., no need for cross-matching of blood type of compatibility testing); free of side effects; non-toxic to the whole organism; reasonable circulation times; non-toxic and excretable without causing harm; no scavenging of nitrous oxide NO from the blood; non-immunogenicity; easily sterilizable to ensure absence of pathogens such as viruses; no interference with ordinary blood components; stable at room temperature and cheap to manufacture in large quantities; long shelf life and immediate full capacity oxygen transport when implemented.
Thus, in view of the many problems experienced with artificial blood products and particulate carriers intended for the controlled delivery of biologically active substances within the body, there is a need in the for improved AOC and particulate carriers that have one or more of the following characteristics: (a) do not break down unexpectedly and allow accidental release of active medicinal substances that may be toxic in unregulated doses in the body, (b) provide adequate oxygen uptake in the lungs and delivery to the tissues and corresponding removal of carbon dioxide from the tissues, (c) non-toxicity to the body, (d) does not scavenge nitrous oxide from the blood, (e) cheap to manufacture, (f) stable at room and low temperatures, (g) long shelf life, (h) free of side effects, (i) does not interfere with ordinary blood components, (j) has wide applicability so there is no need for cross-matching of blood type or compatibility testing, (k) are chemically and biologically inert so they are devoid of biological materials eliminating the possibility of spreading an infectious disease via a blood transfusion, (l) perfluorocarbon-based AOCs that do not have the problems previously experienced in the prior art, and (m) do not have to be tested for diseases.